REST PERIOD STUDIES WITH SEEDS 51 



seeds in a box lined with sand paper. This treatment caused the 

 seeds to make a much better germination. 



Crocker 1 (1907) made germination tests of seeds of aquatic 

 plants. Seeds collected while still green germinated quite readily, but 

 in many instances the dried seeds refused to germinate. This dif- 

 ficulty was overcome by cracking the seed coat. If allowed to become 

 dry, the seeds of many water plants are unable to germinate because 

 the seed coat becomes so hard that it cannot absorb moisture. While 

 such seeds may have a rest period, the chief failure to germinate is 

 due to the hardness of the seed coat. To secure germination this 

 mechanical hindrance must be removed. 



An injury to the seed embryo itself, such as mutilating a coty- 

 ledon, sometimes hastens germination. 2 While the effects of freezing 

 and stratification may in some instances be mechanical in their nature, 

 it is very probable that other changes are also induced by such treat- 

 ments. Stratification is employed for softening the seed coat, and 

 freezing generally assists in this process. Nurserymen find it neces- 

 sary to treat many seeds, particularly of woody plants, by stratifying. 

 Soaking under special conditions will sometimes produce the same 

 results. 



Chemical Stimulation, Various chemical or enzymic solutions 

 have been used to hasten or retard germination. Rostrup 3 used 

 sulphuric acid on seeds of Lathyrus sylvestris securing 100 per cent 

 germination, as compared with 76 per cent in seeds not treated by the 

 acid. 



Todaro 4 also found that sulphuric acid (sp. gr. 1.84) acted upon 

 the hard seeds of many leguminous plants, rendering them capable 

 of prompt germination. He immersed the seeds in the acid for one 

 hour at a temperature of 25 to 28 C. Not only was growth hastened, 

 but also a higher percentage of germination was secured. Thornber 5 

 treated seeds of several species with sulphuric acid in which chomic 

 acid had been dissolved and then neutralized with potassium hydrate. 

 Seeds of acacia, mesquite, locust and others germinated readily. Quick 

 germination was brought about in seeds that were almost impervious 

 to moisture by soaking in water at a temperature of 85 to 88 C. 

 for 2-6 minutes. 



1. Crocker, Botanical Gazette, Vol. 44, pp. 375-380. 



2. Experiment Station Record, Vol. 22, p. 326. 



3. Rostrup, Exp. Station Record, Vol. 10, pp. 53-4. 



4. Todaro, Experiment Station Record, Vol. 12, pp. 754-5. 



5. Thornber, An. Report Arizona Agr. Exp. Sta. 1904, pp. 489-93. 



